CB antenna tuning woes

[Gearhead]

Hi CB experts!

 

My CB has been nothing but a headache from start to...well...I haven't finished yet. Broken antenna, bad squelch and volume pots, SWR meter issues and now tuning problems.

 

I installed a Wilson Flex 3' antenna with tunable tip. I like it better than the Firefly (or did like it better) because the Firefly is much fatter, achieving it's light weight by being hollow. I like the thin-ness of the Wilson aesthetically. I have the 203EZ folding mount. My bracket looks different from some I have seen and I think was adapted off something else. I modified it to move the antenna backward 3", placing it above the very back edge of the RH saddlebag so it the lid wouldn't bang into it when removing. The cable was already on the bike. I am intending to use a Firestik AR-1 duplexer/splitter.

 

Went to tune it this morning, thinking this would be a slam dunk - just mess with the tunable tip and be done. Wrong! I was measuring with the splitter out of the loop, just the CB and antenna. SWR was super high, above 3 on all channels, but a little higher on 40 than on 1, so I lowered the tunable tip. Improved slightly. Finally removed the tunable tip entirely and got readings of 1.7 on 1 and just under 3 on 40. Ch 20 was somewhere in between, in the low 2's. Huh? What gives?

 

Now I know that JB (lonestarmedic) used the same antenna on the same bike and got 1.5 at channels 1 and 40, I have something unique going on. I've studied this on the web, and here's what I already checked:

 

- Bracket ground has 0 ohms to bike frame. Supposedly high SWR is caused by a bad ground plane 90% of the time.

- Just for yuks, I added a ground wire from the bracket to the frame and SWR improved slightly, 1.5 on 1 and 2.5 on 40. The same happens if I hold the bracket with my hand.

- Cable has continuity in the center and in the shield, but no short between the two - like it should be.

- Putting splitter in the circuit made it worse - SWR way over 3 across the board.

- Performed measurements in an open space.

- Connecting the Wilson's "matching transformer" lead to ground made it worse. This makes sense. I don't understand this feature, but Wilson says it will lower the center freqency by 20 channels. My center frequency is already too low; I think it's below channel 1 in fact.

- Tried removing fold-down mount - no change.

- Double-checked how to connect and use the meter.

 

So where do I go from here? Do I need to start removing material from the tip of the Wilson, even though it's supposed to have the full tuning range in the adjustment? What else?

 

Frustrated,

Jeremy

[Condor]

Hi CB experts!

 

My CB has been nothing but a headache from start to...well...I haven't finished yet. Broken antenna, bad squelch and volume pots, SWR meter issues and now tuning problems. Jeremy

 

 

That's a lot of info to digest Jeremy. Lost me half way thru. But gotta ask. When you connected the co-ax to the base of the antenna did you take the shield (outer braided cover) and ground it to the frame. A lot of CBers will use a 3/8ths nut to connect the center to the base of the antenna using a plastic washer to isolate the antenna from the mount and then solder the shield and crimp it into a eye connector and attach it so that it makes contact directly with the mount. Also, I can't remember, but does the radio body need to be grounded also??? Keep getting VHF and CB stuff mixed up. Good luck....

[BOO]

This hard to do without looking at the way you have it hooked up. I will try and answer some of your questions hoping maybe this will help you.

 

 

Hi CB experts!

 

My CB has been nothing but a headache from start to...well...I haven't finished yet. Broken antenna, bad squelch and volume pots, SWR meter issues and now tuning problems.

 

I installed a Wilson Flex 3' antenna with tunable tip. I like it better than the Firefly (or did like it better) because the Firefly is much fatter, achieving it's light weight by being hollow. I like the thin-ness of the Wilson aesthetically. I have the 203EZ folding mount. My bracket looks different from some I have seen and I think was adapted off something else. I modified it to move the antenna backward 3", placing it above the very back edge of the RH saddlebag so it the lid wouldn't bang into it when removing. The cable was already on the bike. I am intending to use a Firestik AR-1 duplexer/splitter.

 

Went to tune it this morning, thinking this would be a slam dunk - just mess with the tunable tip and be done. Wrong! I was measuring with the splitter out of the loop, just the CB and antenna. SWR was super high, above 3 on all channels, but a little higher on 40 than on 1, so I lowered the tunable tip. Improved slightly. Finally removed the tunable tip entirely and got readings of 1.7 on 1 and just under 3 on 40. Ch 20 was somewhere in between, in the low 2's. Huh? What gives?

 

Now I know that JB (lonestarmedic) used the same antenna on the same bike and got 1.5 at channels 1 and 40, I have something unique going on. I've studied this on the web, and here's what I already checked:

 

- Bracket ground has 0 ohms to bike frame. Supposedly high SWR is caused by a bad ground plane 90% of the time.

- Just for yuks, I added a ground wire from the bracket to the frame and SWR improved slightly, 1.5 on 1 and 2.5 on 40. The same happens if I hold the bracket with my hand.

- Cable has continuity in the center and in the shield, but no short between the two - like it should be.

- Putting splitter in the circuit made it worse - SWR way over 3 across the board.

It will, any connection added to the circuit will make the SWR worse and lose signal strength.

- Performed measurements in an open space.

- Connecting the Wilson's "matching transformer" lead to ground made it worse.

Not sure what this is but if it didn't come with the antenna don't use it.

This makes sense. I don't understand this feature, but Wilson says it will lower the center frequency by 20 channels. My center frequency is already too low; I think it's below channel 1 in fact.

You should be trying for your best SWR at channel 20. All things being equal then channel 1 will be higher also channel 40 will be higher, maybe not equally higher, if that makes sense.

- Tried removing fold-down mount - no change.

If you remove the fold-down then the point where your SWR is the best will be higher in frequency. (channel)

- Double-checked how to connect and use the meter.

 

So where do I go from here? Do I need to start removing material from the tip of the Wilson, even though it's supposed to have the full tuning range in the adjustment? What else?

 

No, I wouldn't do that. I think you have something either hooked up wrong, or the meter is hooked up backward or you have a bad ground or you have a bad coax cable or bad connector or loose connector.

Also if there is somewhere where the coax is pinched or has a nick in the outer plastic coating then that can be a problem.

 

Frustrated,

Jeremy

 

Not sure I helped you much but chasing RF problems can be a real challenge sometimes.

I know you mentioned a couple of different things that you have in your circuit, only use components recommended by the antenna manufacture. These would all be matched parts.

Jerry

[Gearhead]

Thanks guys for your input. Condor, I did not directly ground the braided shield, but it is connected to the outer portion of the PL259 connectors which are in direct contact with the antenna bracket (grounded) and CB metal case. The CB case I presume is grounded through the wiring harness, but just for yuks I made a separate ground wire to run from a screw in the case to the frame; it actually made the SWR a little worse.

 

Jerry, regarding the splitter / duplexer, I didn't expect it to drive the SWR so far up. But most of my testing was without the splitter anyway. The "impedance matching transformer" did come with the antenna. As far as I can see it's just a wire with a ring terminal coming out the bottom of the antenna. I'm not using it as it makes my SWR worse. They say to tune without it first and only connect if necessary. When I connect it, things get worse. I did remove the fold down and it had no effect.

 

I ground just a bit off the brass at the top of the antenna (with the tuneable tip removed completely) and it helped slightly. At this point, my lowest SWR is down to about 1.5 at CH1 and it goes up from there; testing it at Ch 2, 3, 4 etc showed a gradual increase to around 2.5 at Ch 40. So I don't have that "dip" in SWR that's supposed to be at Ch 20; my resonant (center) frequency is currently at some frequency below the CB band. I think more material needs to come off the top, but I dunno why my installation wants an antenna that's so "short".

 

My cable buzzes out OK, but I haven't traced the entire length for nicks. I want to hook up another cable and try it.

 

Jeremy

[Rocket]

 

I ground just a bit off the brass at the top of the antenna (with the tuneable tip removed completely) and it helped slightly. At this point, my lowest SWR is down to about 1.5 at CH1 and it goes up from there; testing it at Ch 2, 3, 4 etc showed a gradual increase to around 2.5 at Ch 40. So I don't have that "dip" in SWR that's supposed to be at Ch 20; my resonant (center) frequency is currently at some frequency below the CB band. I think more material needs to come off the top, but I dunno why my installation wants an antenna that's so "short".

 

My cable buzzes out OK, but I haven't traced the entire length for nicks. I want to hook up another cable and try it.

 

Jeremy

 

Been about 15 years since setting SWR, but it was done with the cb set to channel 20, go for the lowest reading there............

[Guest tx2sturgis]

Went to tune it this morning, thinking this would be a slam dunk - just mess with the tunable tip and be done. Wrong! I was measuring with the splitter out of the loop, just the CB and antenna. SWR was super high, above 3 on all channels, but a little higher on 40 than on 1, so I lowered the tunable tip. Improved slightly. Finally removed the tunable tip entirely and got readings of 1.7 on 1 and just under 3 on 40. Ch 20 was somewhere in between, in the low 2's. Huh? What gives?

 

 

Youre 'overthinking' it. If you get the classic dip, and readings like this, it means ONE thing, and one thing only.

 

The antenna is too long. All the other stuff about grounding and matching and everything else is irrelevant, because the meter can only ACCURATELY measure from the meter's antenna port out toward the antenna. Any weird reading you get (from radio grounding to flying leads to matching of the radio) is simply floating RF getting into the meter. Once the meter begins to show some higher/lower readings, its all in the tuning. If it was a bad ground, or a short, you would be seeing a REALLY bad SWR, like infinite or close to it.

 

I suspect, that the wilson is tuned for a standard mount, and you probably have an added inch or 2 of material in the foldover mount that the maker did not take into consideration when designing the antenna (being designed for a standard 3/8 mount, about 1 inch above the feedpoint) Everything above the feedpoint will be counted as 'antenna'...so, you may be OK if you keep that tip out, or just plug it with something that is non-conducting.

 

You might be able to remove some material at the tip or base, I'd have to see it to know for sure.

 

Back in the day, we would mount up a 9 foot bumper whip, and we sometimes had to remove more from the antenna if we used a big spring at the base. That spring added several inches to the antenna, and you would normally have to remove some material to get the tuning 'perfect'...its even more critical with shortened antennas.

 

If the antenna is externally wound, you may want to try carefully removing the cover at the base, short out one turn, then recover with heat shrink tubing.

 

Having said that, I believe the difference is not going to be any greater range. An SWR of about 2 on channel 20 is acceptable. Not great, but good enuff to not hurt anything. The difference in transmit range between 1.5 and 2.0 SWR is barely measurable with a field strength meter, and wont hurt the transmitter at all. Reciever range will be the same either way.

 

Now once you put the splitter back in, thats when the transmitter will be seeing a high SWR and it may not like it. Anyone running a CB/AM-FM splitter ( factory or not) is going to have to settle for reduced performance. Period. No exeptions.

 

If you want maximum performance, you have to run seperate antennas, and go to a 4 or 5 foot whip. Your call.

 

 

 

 

 

Edited May 20, 2008 by tx2sturgis

[GeorgeS]

I agree with TX sturgis. Sounds like the fold over mount, is Increasing the length of your antenna, thus lowering the Resonant Frequency to below ch 1.

 

Also, double check that the mounting of the base to the actual frame of the bike, there might be some High Resistance, not likley, but possible.

 

Can you install your SWR meter between the output of the transmitter, and the Splitter, see what the SWR looks like hooked in that way.

 

 

Another question, are you useing the Old cable, or a New Cable with the New Antenna ?? Might be a problem with the old cable.

[Hugbare]

Doubt it is the Fold-over .. Have used them for the past 9 years on both

1g and RSV installs and have never had one spec of trouble from them, other

than a little slop ever now and then ... I am not really sold on the Wilson antenna.

Have used them once or twice but have always had problem tuning them lower than

1.7:1 at CH 20 and then using that as the lowest dip, would measure 1 and 40 to

ensure they were not above 2.0:1 ... Because of this, have stuck with the Firestik

Firefly and Firestik II antennas ... My latest adventure has been on the Honda ST1300.

99% of the owners who have install CB's have gone with the NGP (No Ground Plane)

antennas .. Reckon they work OK, but went the old fashion way, and used the 2'

Firestik II antenna .. SWR tuning was right in line with what I have found on the

1g and RSV ..

 

Personally from what I have read here, I am betting on the Antenna not being compatible

for use on a bike ... It happens .. KA KA Occurs !!!

[calperin]

Jeremy,

 

Can you check if your antenna use ground plane? Bike antennas shouldn't be using it, since it is almost impossible to define it.

 

It is not like cars or trucks where the antenna is mounted on a flat metal plane.

 

You can check it releasing the antenna from the bike, grounding it to the bike, but moving around with the SWR on it.

 

I have a J&M radio with this kind of antenna, and worked perfect after adjust the cable with the SWR.

 

Let us know,

 

Carlos

[BOO]

Interesting thread although I doubt it's helping fixing his problem with the antenna.

Someone through in a new term to me NGP antenna, can I presume that's a dipole type antenna? I know some of the Cell Phones use dipole's and I'm pretty sure the antenna's used for boating must be dipoles? Unless the water is being used for the ground plane?

Sorry about stealing the thread,

Jerry

[calperin]

Jerry,

 

Yes, dipole antennas are no ground plane antennas. With that you don't need to have your system grounded to the earth, or something huge enough to work as a ground.

I don't mean an electrical ground, I 'm talking a propagation ground, like the earth.

 

Most of mobile system uses this type of antennas in order to increase gain, and minimize the use of transformers, or adaptation coils.

 

Of course, are not the favorites of the manufacturers since your antenna system become much cheaper.

 

It is easy to test if this is the problem changing the position of the antenna regarding the bike. enough to move it about 4 feets away, like 4 o 6 inches at the time.

 

Regars,

 

Carlos

[Marcarl]

My first question would be, did you alter the coax at all, and the second thought goes to: Is the frame of you bike grounded properly. Find the ground strap that goes from the frame to the engine and clean the ends, if you can't find one, then make one. I put one between the grounding screw, right front side of the engine to the bolt that holds the cross member in place in front of the rad. That improved frame grounding noticeably.

[Gearhead]

Well, I removed the fold-down with no effect - still SWR 1.5 to 1.7 at Ch 1, moving right up to 2.5 to 3 at Ch 40. But I see the logic in removing it until I get good results, then try adding it back in.

 

TX, I'm not doing my testing with the splitter yet, other than a quick test. That may cause me problems, but it's not the present issue.

 

Hugbare, we have a guy, JB or lonestarmedic, who used this antenna with acceptable results - SWR 1.5 or so (can't remember if that was at 1 and 40 or at Ch 20). He did not use a splitter or fold-down.

 

George and Carl, the cable was already there, I haven't touched it except to buzz it out. I do not think it's stock; it had dual 16" antennas and un-stock mounts when I bought it and I think the cable was installed with that mod. I need to check that it's RG58, and I'd like to try another cable.

 

George, I've checked for resistance from the cable shield to the bracket to the chassis, and there isn't any. Most of my testing has been wired like this: CB - 1' jumper cable - SWR meter - bike antenna cable - mount and fold-down - antenna. No splitter at all. I briefly tried it with the splitter installed between the SWR meter and the bike antenna cable, results were very bad. I will look at that more after the antenna itself is tuned right.

 

Carl, I have cleaned and added grounds over the last year to improve charging performance and reduce headset noise, which I did succeed in doing (although there's still a bit of persistent noise - arrghhh).

 

Carlos, plenty of people use standard, ground-plane-type CB antennas on bikes. It's not the ideal ground plane but it seems to work for most people. Why wouldn't it work for me? That being said, I have read about the NGP kits from Firestik and others. What they do is change the way the cable shield is connected such that it is totally isolated from ground and the shield actually becomes the ground plane. Thus, it requires a special cable. This according to Firestik's tech page.

 

Thanks guys, this gives me more ideas and stuff to look at. Still looking for all the help I can get! My Dad is about to install a CB on his Voyager, and as such he is going to buy an antenna (different from mine) and a cable, so I can sub those in and try them. Maybe that's the logical next step.

 

Jeremy

[GeorgeS]

This feed line cable, you said was Installed by a previous owner. !!!

 

Check the End Plugs, on both ends. Does it look like a Home Made Cable ??

 

Or, commercially made cable.

 

If, home brew, I would open up the plugs on each end, and carefully check the soldering job !!! ( If they are not crimped on) But I would still be suspicious.

 

I have made up a lot of these cables over the years, its very easy to screw them up, and there are Several types of connectors.

 

Just because it Ohms out OK, does not mean its perfect.

 

These cables also can get Moisture inside them, with age.

 

If you make up a new cable, And if your Antenna is a 1/4 Wave ground plane, then your feed line, should be an ODD number of 1/4 wave lengths.

 

Go to the Fire Stik, web site, they give a lot of good information there, as to Feed lines, and makeing up the cables.

[Guest tx2sturgis]

Well, I removed the fold-down with no effect - still SWR 1.5 to 1.7 at Ch 1, moving right up to 2.5 to 3 at Ch 40. But I see the logic in removing it until I get good results, then try adding it back in.

 

TX, I'm not doing my testing with the splitter yet, other than a quick test. That may cause me problems, but it's not the present issue.

 

 

Hey gear...a reading of 1.7 is not that bad...it means your grounds and such are probably in good shape. It tells you that its a matter of tuning, more than troubleshooting for opens and shorts.

George and Carl, the cable was already there, I haven't touched it except to buzz it out. I do not think it's stock; it had dual 16" antennas and un-stock mounts when I bought it and I think the cable was installed with that mod. I need to check that it's RG58, and I'd like to try another cable.

If the bike had dual antennas, and the owner used a co-phase harness, you need to get rid of that. Its the wrong impedance. Replace with 50 ohm cable.

 

George, I've checked for resistance from the cable shield to the bracket to the chassis, and there isn't any. Most of my testing has been wired like this: CB - 1' jumper cable - SWR meter - bike antenna cable - mount and fold-down - antenna.

RF travels mostly on the SURFACE of a conductor, and if the cable is old and deteriorated, or oxidized, the performance will decline. DC wont care how it travels along the conductors, so although testing with a continuity tester will help you find shorts and opens, it wont tell you if the cable is RF 'friendly'. Coax is a wear item, believe it or not. Moisture migrates into the braid and oxidizes it, (RF hates that!) unless it is perfectly sealed from the elements. Otherwise, it has to be replaced every few years.

 

Carlos, plenty of people use standard, ground-plane-type CB antennas on bikes. It's not the ideal ground plane but it seems to work for most people. Why wouldn't it work for me? That being said, I have read about the NGP kits from Firestik and others. What they do is change the way the cable shield is connected such that it is totally isolated from ground and the shield actually becomes the ground plane. Thus, it requires a special cable. This according to Firestik's tech page.

 

As long as you provide a counterpoise, it should work. Whether its frame type groundplane or a coax shield or a seperate non-terminated wire running from the mount to the front of the bike, the antenna will be happy. Try attaching a 9 foot wire to the mount, just for grins, then test it again. Also, be aware that 'near-field' metallic objects (like a trunk with a rack) can cause severe de-tuning.

Thanks guys, this gives me more ideas and stuff to look at. Still looking for all the help I can get! My Dad is about to install a CB on his Voyager, and as such he is going to buy an antenna (different from mine) and a cable, so I can sub those in and try them. Maybe that's the logical next step.

 

Jeremy

Its always a good idea when troubleshooting, to practice RKG. Replace with Known Good. Swapping out a known good antenna, or cable just for testing, will help narrow down the culprit. I'd love to hook up my Antenna Analyzer to this one...we'd figure out the situation in just a few minutes.

 

Good luck.

[Gearhead]

Hey TX, thanks, and I would have loved to have your help with your antenna analyzer, whatever that is! And the previous dual antennas were individual, one for radio and one for CB.

 

Thanks to all who chipped in. Your input and ideas have helped me understand CB's better. Special thanks to Lonestarmedic and Hugbare for your continued assistance.

 

Problem solved! Friend Richard who's an old-time CB'er, my Dad, and I spent several hours on it Saturday and life is good. To cut to the chase, the antenna was way too long electrically for my installation, don't know why. I had already removed the tunable tip, and had to cut about 3/4" off the brass slug at the tip where the tunable tip used to go. My SWR is below 1.3:1 on all channels.

 

It took us awhile to get there. Richard had never run into a situation before where the antenna was so far out of tune, so we needed some convincing that "too long" was really the problem. With the tunable tip removed, SWR was 1.5 to 1.7 on CH1 and almost 3 on CH40. My dad bought the stuff for his antenna, so we did the RKG method. We substituted for the cable, mounting stud, and even tried a different CB with no change. Dad's new antenna, a base-loaded 4' whip, was actually worse. We tried different supplemental grounding schemes for the antenna bracket. We checked the meter with a dummy load and it was good. We removed the fold-down and had already removed the splitter. All with no change.

 

So we started cutting the brass tip, 1/8" at a time. After the first cut it was clear we were doing the right thing. A little more, a little more, and finally, approx. 3/4" later, CH40 came down and there was a dip in the middle (CH20). Put the fold-down back in with no change. Made sure everything was hooked up and routed back the way I wanted it. We got the SWR as low as about 1.1 on CH1 and 40, with barely a twitch of the needle at CH20.

 

Then I put the splitter back in, a Firestik AR1 Matchmaker. SWR went WAY up - like over 3. I was not optimistic as I reached for the little tuning tool they supplied. But after some tweaking on the CB pot, I had the SWR down to ~1.35 at 1 and 40. Then I discovered that the Radio pot on the splitter didn't really affect radio reception, but it did fine-tune the CB SWR - go figure. I was able to get SWR down to about 1.25 on 1 and 40 with the splitter in place. Wow - I thought I'd never get there.

 

Wilson tech never got back to me, despite two emails and two phone calls. Thanks a heap, Wilson! But I like their antenna.

 

Jeremy

[Hugbare]

That is outstanding news ... Had only used the Wilson once long time ago

and remembered we had a lot of trouble getting the SWR right .. Glad it

all worked out for you and will remember these steps in case the Firefly

ever gives me trouble .. So far on the Firestik Firefly and Firestik II have

had no difficulty at all ...